1. Field of the Invention
This invention relates to anti-theft devices and systems for protecting articles against pilferage. More particularly, this invention relates to anti-theft devices which contain a detectable chemical agent and to systems which are capable of detecting that chemical agent.
2. Description of the Prior Art
Flexible plastic fasteners for attaching a sales tag to an article are well known. A brochure entitled "Swiftach.TM. Systems for tag attaching," published by Dennison Manufacturing Company, Framingham, Mass., 1977, illustrates several such fasteners. The fasteners are nonreusable and must be cut or broken before they can be removed. These fasteners "offer maximum security against `would be ticket switchers`", according to the brochure. However, these fasteners do not prevent a dishonest customer or employee from removing the tag from the article unobserved (as for example in a dressing room) and leaving the store with the article.
Various types of systems for detecting unauthorized removal of an article from a protected area are also known. Such systems monitor the passage of a protected article through the exit doorway of a protected area such as a store. One such type of system (probably the type enjoying the greatest commercial acceptance at present) comprises a radio transmitter and receiver typically located near the exit (or exits) from the protected area, and a "passive" device or tag attached to each article to be protected. When a shoplifter attempts to take a tagged article through a protected exit, the tag receives a signal from the transmitter and reradiates a signal of a frequency different from the transmitter frequency. The receiver picks up the reradiated signal and causes an alarm to sound. Representative systems of this type are described in Welsh et al. U.S. Pat. No. 4,063,229 and in the copending commonly assigned application of Harold B. Williams, Ser. No. 373,251, filed Apr. 29, 1982, now allowed.
Theft detection systems employing chemical agents have been described in only a few references and such systems have not gained commercial acceptance. One such system, used for monitoring exits, is described in Haynes U.S. Pat. No. 3,725,895. In this system, the article to be protected is sprayed with an aerosol spray which contains a detectable chemical agent, e.g., a "Freon" compound microencapsulated in a polymer matrix. Presence of the chemical agent may be detected electronically, e.g., by a gas chromatograph equipped with an electron capture detector placed near a store exit. A second chemical agent, applied by a cashier at the time of sale, indicates that the article has been purchased. If the detector detects only the first chemical agent, indicating a theft, an alarm sounds.
Another device employing a chemical agent is shown in Allen U.S. Pat. No. 3,272,533. This device, which is described as being useful to indicate theft of paper money and other negotiable paper, comprises a brittle (glass or brittle plastic) tube containing a chemical agent having a distinctive odor. The tube is secured to a bill by an adhesive. Breakage of the tube (either intentionally by a teller or unintentionally by a thief) during handling of the money releases the chemical agent. The agent may be detected by human or canine sense of smell. A disadvantage of this is that the tube may be broken unintentionally in normal handling.
Systems for protecting exit doors give no protection against a thief who removes the tag from the protected article while still inside the store. One answer to this problem is the widespread use of tags having locks which require a special tool in order to remove the tag from the protected article. Such tags are expensive: also, they subject the customer to considerable inconvenience if (as sometimes happens) the sales clerk forgets to remove the tag at the time of sale. Also, such locks do not deter thefts by store employees to any appreciable extent, since many store employees have access to the special tools required to unlock the tags.